When sulphonamides are prepared in aqueous phase, an aqueous sulphonamide solution is finally obtained, which, in order to be able to isolate the sulphonamide, must be concentrated so as to crystallize the sulphonamide. Unfortunately, the aqueous solution to be concentrated generally contains salts, in particular ammonium chloride, which makes this concentration step difficult.
The prior art does not mention the use of membrane techniques in processes for the synthesis of sulphonamides, which, such as that of patent FR 2,708,266, use reactions carried out in a solvent medium such as acetonitrile or propionitrile.
The use of electrodialysis membranes to desalinate aqueous solutions is known to those skilled in the art and forms the subject, in particular, of patent EP 536,021, which relates to the desalination of aqueous solutions of polar aprotic solvents.
Application of this technique to the desalination of aqueous sulphonamide solutions derived from an aqueous-phase synthetic process is, however, unknown. Given that the sulphonamides concerned (in particular MSAM) have a relatively low molecular mass, they are liable to diffuse considerably across the membranes and it might be feared that high desalination yields could not be obtained.